Global Systems: Insolation and Factors Affecting It

Learning Goals

• Define solar insolation.
• Determine the relationship between latitude and solar insolation.
• Interpret scatter graphs to identify relationships in a data set.
• Extrapolate data from a scatter graph to draw conclusions.
• Use data tables and graphs to identify specific values, trends, and relationships.

Factors Affecting Air Temperature

• The major factor affecting air temperature is insolation.
• Air temperature varies among latitudes and at different times of the year due to insolation.

What is Insolation?

• Insolation is solar radiation that is received in the atmosphere or on the Earth’s surface.
• The sun constantly releases energy in all directions, known as solar radiation.

Distribution of Insolation

• The distribution of insolation on the Earth’s surface is uneven.
• In general, insolation received declines with increasing latitude.
• Areas around 23.5° N and S receive the highest value of insolation.

Factors Affecting Insolation Received

• Angle of the sun
• Duration of daylight
• The atmosphere
• Latitude
• Time of day
• Season

Angle of the Sun

• The angle of the sun refers to the angle at which sunlight strikes the Earth’s surface.
• It varies with the latitude of a location and with the time of day.
• When the sun is directly overhead (angle of the sun is 0°), it is known as the overhead sun.
• A simple experiment can demonstrate how the angle at which the sun strikes a location impacts the amount of solar insolation it receives.

Relationship Between Angle and Insolation

• High Angle (0° / Right angle):
  • Smaller area to warm up.
  • High/More intense insolation.
• Low Angle (>0° / Acute angle):
  • Larger area to warm up.
  • Low/Less intense insolation.

Latitude and Insolation Angle

• Low-Latitude Regions:
  • The angle of the sun is larger.
  • Insolation concentrates on a smaller area.
  • Insolation is stronger.
• High-Latitude Regions:
  • The angle of the sun is smaller.
  • Insolation concentrates on a larger area.
  • Insolation is weaker.

Time of Day and Insolation

• The angle of the sun is also impacted by the time of day.
• In the Northern Hemisphere around the spring equinox:
  • The angle of the sun increases until it reaches a maximum at noon (midday sun).
  • Then, the angle of the sun decreases.
  • The amount of insolation received will be lower in winter.

Seasons and Insolation in Hong Kong

• Summer Solstice:
  • The overhead sun is located at the Tropic of Cancer, which is close to Hong Kong.
  • Hong Kong receives the largest amount of insolation.
• Autumnal Equinox:
  • The overhead sun is located at the Equator.
  • Hong Kong receives less insolation in autumn than in summer.
• Winter Solstice:
  • The overhead sun is located at the Topic of Capricorn.
  • Hong Kong receives the least amount of insolation.
• Spring Equinox:
  • The overhead sun is located at the Equator.
  • Hong Kong receives more insolation in spring than in winter.

Duration of Daylight

• The longer the duration of daylight, the more insolation received.
• In equatorial regions, the duration of daylight is almost 12 hours daily throughout the year.
• In polar regions, daylight can last for 24 hours in summer, while in winter, there is no sunlight at all.

The Atmosphere

• Dust particles, gas molecules, and clouds in the atmosphere can reflect, absorb, or scatter solar radiation.
• Only about 58 units of solar radiation reach the Earth’s surface.
• Maximum insolation received occurs at around 23.5° N and S but not at the Equator, because:
  • The amount of cloud cover in the equatorial regions is high, so much of the solar radiation is reflected by clouds, reducing insolation reaching the Earth’s surface.
  • The climate is drier, and there is less cloud cover at around 23.5° N and 23.5° S, allowing the Earth’s surface to receive more insolation.

Solar Insolation Experiment

• A 10W bulb was used in the experiment.
• Calculate the solar insolation in W/cm^2 for each angle.

Experiment Results:

• Calculate the mean “solar” insolation in W/cm^2 for each angle and create a line of best fit.